/Engine/Source/Runtime/Landscape/Public/LandscapeEdit.h
Without data interpolation, able to get normal data.
template<typename TStoreData> void GetHeightDataTemplFast ( const int32 X1, const int32 Y1, const int32 X2, const int32 Y2, TStoreData & StoreData, [UTexture2D](API\Runtime\Engine\Engine\UTexture2D) * InHeightmap, TStoreData * NormalData )